This invention relates generally to treating the surfaces of the teeth to make them adhesive to acrylic resin and, more specifically, to treating the surfaces of the teeth for restoring them and bonding dental composite material (composite resin) to them.
With a conventional adhesive for bonding restorative composite resin to enamel, a bonding strength higher than 100 kg/cm.sup.2 that meets clinical requirements well enough is obtained between enamel and the restorative composite resin. This is true even when enamel is treated by acid etching using phosphoric or citric acid, then washed with water and dried, and finally coated with a bonding material which is composed of a methacrylic ester monomer and a curing agent and shows no adhesion to dentin. However, as only poor adhesion to dentin is obtained by using such bonding material having no adhesion to dentin, benzoyl peroxide/an aromatic tertiary amine/sulfinic acid initiators, etc. have been proposed in the art, as set forth Japanese Patent Publication Nos. 56-33363 and Japanese Patent Publication No. 15468. Still, no sufficient bond strength to dentin is obtained at all.
Various dentin treatment solutions or primers which have been said to have adhesion have been proposed. For instance, Japanese Patent Publication No. 55-30768 describes phosphoric ester compounds as being adhesive to dentin, but it fails to give the aforesaid high bonding strength, as measured by the present inventors. Japanese Patent Laid-Open No. 54-12338 discloses a functional monomer 4-methacryloxyethy trimellitic anhydride (hereinafter 4-META for short), and "Journal of the Japan Society for Dental Apparatus and Materials", 23(61), pp. 29-32 (1982) teaches that when dentin is treated with an aqueous solution of 10% citric acid and 3% ferric chloride and then restored with a restorative filler (4-META-containing methyl methacrylate/tri-n-butylborane/polymethyl methacrylate), a bonding strength of 12-18 MPa is obtained. When measured by the present inventors, however, such a high bonding strength could not be obtained.
On the other hand, it has turned out that (thio)barbituric acid derivative/copper compound/chlorine ion-based initiators are considerably effective in terms of bond strength to dentin. In this regard, see "the Journal of the Japan Research Society of Dental Materials and Appliances", Vol. 8, Special Issue No. 14, pp. 89-90 (1989).
However, they have quite the same problem as tri-n-butylborane in terms of the pre-treatment of a tooth surface; that is, they are troublesome to handle and, in addition, does not give sufficient bond strength. Thus, there is left much to be improved.
In view of the present state of the art where no clinically efficacious bonding material is obtained as yet, as already mentioned, we have investigated how to improve adhesion to dentin and, as a result, have accomplished the present invention.